Manufacturing method of display device

ABSTRACT

In forming four liquid crystal panels on a glass substrate, layout is so made that peripheral driving circuit areas of the respective panels are opposed to each other. With this layout, the peripheral driving circuit areas, which are prone to be affected by particles, are prevented from existing in regions close to the perimeter of the glass substrate. This allows liquid crystal panels to be produced at a high yield, as well as enables efficient use of the glass substrate.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a manufacturing method of adisplay device having a pixel area and a peripheral driving circuit areaand, more specifically, to a manufacturing method of an active matrixtype liquid crystal display device.

[0003] 2. Description of the Related Art

[0004] An active matrix liquid crystal display device is conventionallyknown. In the active matrix liquid crystal display device, a structureis known in which a pixel area having pixels that are arranged in amatrix form and a peripheral driving circuit for driving thin-filmtransistors that are arranged in the pixel area are integrated on thesame substrate.

[0005]FIG. 1 shows a general configuration of a panel of an activematrix liquid crystal display device in which a pixel area and aperipheral driving circuit area are integrated on a glass substrate 101.Reference numeral 102 denotes a pixel area in which pixels are arrangedin a matrix of several hundred by several hundred. The fundamentalconfiguration of the pixel area 102 is such that source lines 104 andgate lines 105 are arranged in a matrix form, thin-film transistors 106are arranged at each intersection of the source and gate lines, and thedrains of the thin-film transistors 106 are connected to electrodes(pixel electrodes) for applying an electric field to a liquid crystal107.

[0006] Reference numeral 103 denotes a peripheral driving circuit areafor driving the thin-film transistors for the respective pixels. Theperipheral driving circuit area 103 is also constituted of thin-filmtransistors. The standardized configuration of the peripheral drivingcircuit includes a shift register circuit and an analog buffer circuitthat allows a low-impedance current flow.

[0007] In general, plural panels of the active matrix liquid displaydevice shown in FIG. 1 are produced at the same time by forming aplurality of FIG. 1 configurations on a large glass substrate and thencutting the glass substrate, because this method can reduce themanufacturing cost from the case of producing the panel of FIG. 1 one byone.

[0008]FIG. 2 shows a general layout of active matrix liquid crystaldisplay panels. That is, in FIG. 2, a single glass substrate 101 isallocated to four active matrix liquid crystal display panels 201 to204. The number of panels to which a single glass substrate is allocatedis not limited to four, but may be set as desired.

SUMMARY OF THE INVENTION

[0009] The layout as shown in FIG. 2 can provide an advantage that themanufacturing cost of the active matrix liquid crystal display devicecan be reduced. However, it has been found that if panels are actuallyproduced with the layout as shown in FIG. 2. failures likely occur witha particular tendency.

[0010] For example, if the single glass substrate 101 is allocated tothe foul panels 201 to 204 in the manner shown in FIG. 2, failures occurat a high probability in the panels 201, 203 and 204. The reason isexplained as follows. It has been found that where the active matrixliquid crystal display panel of FIG. 1 is produced singly, more than 80%of circuit failures occur in the peripheral driving circuit area 103.Further, observations with an optical microscope have revealed thatfailures are caused mainly by particles.

[0011] The fact that failures occur in the peripheral driving circuitarea 103 at a high probability attributes to two concurrent factors.First, the peripheral driving circuit area 103 has a much higher degreeof integration than the pixel area 102. The second factor is as follows.In general, as exemplified in FIG. 9, a thin-film transistormanufacturing process includes many steps. For example, when a substrateis moved in a transition from one step to the next, minute particlesfall on the substrate more likely in a region closer to the perimeter ofthe substrate.

[0012] Since the peripheral driving circuit area 103 has a higher degreeof integration than the pixel area 102 as described above, a failure iscaused by particles at a higher probability in the peripheral drivingcircuit area 103. On the other hand, where semiconductor devices areformed on a single substrate, particles (dust) are distributed on thesubstrate in each step (in general, semiconductor devices are formedthrough many steps) at a higher percentage in a region closer to theperimeter of the substrate. Therefore, when a panel is produced as shownin FIG. 1, a failure occurs at a higher probability in the peripheraldriving circuit area 103. Once a failure occurs in the peripheraldriving circuit area 103, no signal current flows through a gate line ora source line that is connected to a location of failure, resulting in aline defect. Even if the failure does not cause a line defect, it willcause a flicker on the screen or an unclear display.

[0013] Now, where the respective cells are produced with the layout ofFIG. 2, it is seen that the peripheral driving circuit areas 205, 207and 208. which themselves are prone to a failure due to particles, existin regions close to the perimeter of the glass substrate 101 in whichregions particles occur at a high probability. Thus, it is understoodthat failures occur at a high probability in the peripheral drivingcircuit areas 205, 207 and 208.

[0014] Based on the recognition of the foregoing problem, an object ofthe present invention is to provide a technique of suppressing failuresin a case where a plurality of panels are produced from one substrate asshown in FIG. 2.

[0015] According to one aspect of the invention, there is provided amethod for manufacturing a panel that constitutes a liquid crystaldisplay device in which a pixel area and a peripheral driving circuitarea are formed in an integral manner on a substrate having a insulatingsurface, wherein layout is so made that a distance between the perimeterof the substrate and the peripheral driving circuit area is longer thana distance between the perimeter of the substrate and the pixel area.

[0016] In the above method, usually a glass substrate is employed as thesubstrate having an insulating surface. Alternatively, a quartzsubstrate or a resin substrate may also be used.

[0017] The pixel area has a number of pixels that are arranged in amatrix form. Each pixel has at least one switching thin-film transistorand, if necessary, a holding capacitor. The peripheral driving circuitarea includes circuits for driving the thin-film transistors in thepixel area. The peripheral driving circuit may includes thin filmtransistors formed on the same substrate as the switching transistors.

[0018]FIG. 7 shows a specific example of the feature “layout is so madethat a distance between the perimeter of the substrate and theperipheral driving circuit area is longer than a distance between theperimeter of the substrate and the pixel area.” The example of FIG. 7 isdirected to a case of producing four panels from a glass substrate 101.In this case, distances a and b between the perimeter of the glasssubstrate 101 and a peripheral driving circuit area 701 are set largerthan distances a′ and b′. A similar layout may be used for a case wherethe number of panels produced from a single substrate is lager thanfour. In accordance with a preferred embodiment of the invention, whenthe substrate 101 is 127 mm×127 mm, the distance a′ and b′ from theperiphery of the substrate 101 to the pixel areas should be at least 10mm so that the minimum quality of the thin films can be guaranteed.Also, the distance a and b from the periphery of the substrate 101 tothe peripheral circuit region should be at least 1.5 times larger thanthe distance a′ and b′. Also, the distance c and c′ is preferably 5 mmor smaller.

[0019] According to another aspect of the invention, there is provided amethod for simultaneously manufacturing four panels that constituterespective liquid crystal display devices in each of which a pixel areaand a peripheral driving circuit area are formed in an integral manneron a single substrate having a insulating surface, wherein layout is somade that the peripheral driving circuit areas of the respective panelsare opposed to each other.

[0020]FIG. 3 shows a specific example of the above method, i.e., alayout for producing four panels from one glass substrate 101. In FIG.3, layout is so made that peripheral driving circuit areas 305 to 308are opposed to each other.

[0021] Where a and b are set larger than a′ and b′ as shown in FIG. 7,the rate of occurrence of failures in the peripheral driving circuitareas 701 to 703, which have a high degree of integration and are asmuch prone to be affected by particles, can be reduced. In addition, itbecomes possible to use the substrate 101 more efficiently.

[0022] Where layout is so made that the peripheral driving circuit areas305 to 308 are opposed to each other as shown in FIG. 3 in producingfour panels from one substrate 101, occurrence of failures in theperipheral driving circuit areas 305 to 308 can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 shows a general configuration of a panel of an activematrix liquid crystal display device incorporating peripheral drivingcircuits;

[0024]FIG. 2 shows a conventional layout of panels that constituteactive matrix liquid crystal display devices;

[0025]FIG. 3 shows a layout of panels that constitute respective activematrix display devices according to a first embodiment of the presentinvention;

[0026]FIGS. 4A to 4D and FIGS. 5A to 5C are sectional views showing amanufacturing process of a panel that constitutes an active matrixliquid crystal display device according to the first embodiment;

[0027]FIG. 6 shows a layout of panels that constitute respective activematrix display devices according to a second embodiment of theinvention;

[0028]FIG. 7 shows a layout of panels that constitute respective activematrix display devices according to a third embodiment of the invention;

[0029]FIG. 8 shows a layout of panels that constitute respective activematrix display devices according to a fourth embodiment of theinvention; and

[0030]FIG. 9 is a flow chart generally showing the manufacturing processof FIGS. 4A to 4D and FIGS. 5A to 5C.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Embodiment 1

[0032]FIG. 3 shows a layout of substrates which constitutes an activematrix liquid crystal display device according to this embodiment. Thisembodiment is directed to a case of allocating one glass substrate 101to four panels. In FIG. 3, reference numerals 305 to 308 denoteperipheral driving circuit areas and 301 to 304 denote pixel areas.

[0033] With the layout of FIG. 3, most part of the peripheral drivingcircuit areas 305 to 308, which are prone to a failure due to theexistence of particles, can be located in regions of the substrate 101where particles exist at a relatively low probability. Therefore, theoccurrence of failures due to the existence of particles can besuppressed from the case of the layout as shown in FIG. 2.

[0034] In the configuration of FIG. 3, distances a and b can be setequal to each other. To efficiently using the substrate 101, it ispreferred that the distances a and b be set as short as possible withina range of not reducing the yield. Since the pixel areas 301 to 304 areless likely affected by particles than the peripheral driving circuitareas 305 to 308, the distances a and b can be set relatively short. Adistance c can be set shorter than the distances a and b.

[0035] It should be noted that where panels produced with the layout ofFIG. 3 include two pairs of panels having an opposite positionalrelationship between the peripheral driving circuit area and the pixelarea.

[0036]FIGS. 4A to 4D and FIGS. 5A to 5C show a manufacturing process ofa panel in which a peripheral driving circuit area and a pixel area areformed on the same substrate, i.e., a panel incorporating peripheraldriving circuits. FIG. 9 is a flow chart generally showing the sameprocess.

[0037] More specifically, FIGS. 4A to 4D and FIGS. 5A to 5C shows aprocess of simultaneously forming a thin-film transistor CMOS circuitthat constitutes a peripheral driving circuit area and N-channelthin-film transistors in a pixel area. Each of FIGS. 4A to 4D and FIGS.5A to 5C is part of a cross-section taken along line A-A′ in FIG. 3.

[0038] First, a silicon oxide film 402 as an undercoat film is depositedon the surface of a glass substrate 401 by sputtering at a thickness of3,000 Å, for instance. An amorphous silicon film 403 is depositedthereon by plasma CVD or low-pressure thermal CVD at a thickness of 500Å, for instance. The amorphous silicon film 403 is crystallized byilluminating it with laser light. This results in a structure shown inFIG. 4A. Alternatively, the amorphous silicon film 403 may becrystallized by heating, or a combination of heating and laser lightillumination.

[0039] By patterning the crystallized silicon film, active layers 404and 405 to constitute a CMOS circuit of the peripheral driving circuitsand an active layer 406 to constitute an N-channel thin-film transistorin the pixel area are obtained. This results in a structure shown inFIG. 4B.

[0040] Thereafter, a silicon oxide film 407 to serve as a gateinsulating film is deposited by sputtering at a thickness of 1,000 Å,for instance. A film mainly made of aluminum and containing a very smallamount of scandium is formed thereon by sputtering or electron beamevaporation at a thickness of 6,000 Å, for instance. By patterning thefilm just formed, gate electrodes 408 to 410 are formed.

[0041] Subsequently, the substrate is subjected to anodic oxidation inan electrolyte in which the gate electrodes 408 to 410 are used asanodes, to form oxide layers 411 to 413 having a thickness of 2,000 Å,for instance. This results in a structure shown in FIG. 4C. The oxidelayers 41 to 413 will become a mask in a subsequent impurity ionimplanting step, that is, will serve to form offset gate regions.

[0042] Thereafter, P+ ions (phosphorus ions) are accelerated andimplanted into the active layers 404 to 406 by ion doping or plasmadoping. (FIG. 4D)

[0043] After a prescribed area is covered with a resist mask 400, B+ions (boron ions) are accelerated and implanted by plasma doping or iondoping. (FIG. 5A) After the resist mask 400 is removed, laser light isapplied to re-crystallize the regions where impurity ions have beenimplanted and to activate the introduced impurity ions. (FIG. 5B)

[0044] Thus, a source region 414, a channel forming region 416, a drainregion 417, and offset gate regions 415 of a P-channel thin-filmtransistor (PTFT) 426, and a drain region 418, a channel forming region420, a source region 421, and offset gate regions 419 of an N-channelthin-film transistor (NTFT) 427 are formed. The P-channel thin-filmtransistor 426 and the N-channel thin-film transistor 427 constitute aCMOS circuit, which is part of peripheral driving circuits.

[0045] Further, a source region 422, a channel forming region 424, adrain region 425, and offset gate regions 423 of an N-channel thin-filmtransistor (NTFT) 428 are formed at the same time as the above TFTs 426and 427.

[0046] Subsequently, a silicon oxide film as an interlayer insulatingfilm 429 is deposited by plasma CVD at a thickness of 7,000 Å, forinstance. After contact holes are formed, source wiring lines 430, 432and 433, and a drain wiring line 431 are formed with aluminum or someother appropriate metal material. The drain wiring line 431 is common tothe PTFT 426 and the NTFT 427, which constitute the CMOS circuit.Further, an ITO electrode 434 is so formed as to extend to a pixelelectrode. A protection film 435 is then formed. Thus, as shown in FIG.5C, the peripheral driving circuit area and the pixel area aresimultaneously formed on the glass substrate 401.

[0047] Thereafter, the respective panels are cut out to produceindividual panels. Thus, the panels to constitute active matrix liquidcrystal display devices can be obtained.

[0048] Embodiment 2

[0049] This embodiment is directed to a case of producing two panelsfrom one glass substrate. FIG. 6 shows a general layout of thisembodiment. In FIG. 6, reference numerals 603 and 604 denote peripheraldriving circuit areas and numerals 601 and 602 represent pixel areas.With the configuration of FIG. 6, the yield of the panel formation canbe increased by making a′ longer than a. That is, by making thedimension a′ long. which considerably affects the rate of occurrence offailures, the reduction of the utilization ratio of a substrate 101 canbe minimized as well as the yield can be made high. As for dimensions a,b and b′, a relationship b≈b′≈a may be established in terms of minimumnecessary values. Distance c can be set smaller than a, a′, b and b′.That is, a relationship a, a′, b, b′>c can be established.

[0050] While the relationships among a, a′, b, b′ and c are given asdescribed above, specific values of these parameters depend on anecessary yield, conditions of device manufacturing process, and thecleanliness of the process and need to be determined experimentally.

[0051] Embodiment 3

[0052] This embodiment is directed to a case of producing four panelsfrom one glass substrate 101 with a layout shown in FIG. 7. In FIG. 7,reference numerals 701 to 704 denote peripheral driving circuit areasand numerals 705 to 708 represent pixel areas. With the layout of FIG.7, the rate of occurrence of failures due to particles that fall on theperipheral driving circuit areas 701 to 704 can be suppressed byestablishing a relationship a′<a and b′<b. At the same time, by makinga′ and b′ short, panels can be produced with efficient use of the glasssubstrate 101. Relationships a≈b and a′≈b′ may be established. Distancesc and c′ can be set shorter than a, a′, b and b′, that is, can beselected within such ranges as to satisfy a relationship c, c′<a, a′, b,b′. Further, a relationship c=c′ may be established.

[0053] With the layout of FIG. 7, the positional relationship betweenthe peripheral driving circuit area and the pixel area can be madeidentical in any of the panels. Therefore, this layout is advantageousover the layout of FIG. 3 in being capable of producing panels havingthe same configuration.

[0054] Embodiment 4

[0055] This embodiment is directed to a case of producing two panelswith a layout shown in FIG. 8. In FIG. 8, reference numerals 801 and 802denote peripheral driving circuit areas and numerals 803 and 804represent pixel areas.

[0056] With the layout of FIG. 8, the rate of occurrence of failures inthe peripheral driving circuit areas 801 and 802 can be suppressed byestablishing relationships a>a′ and b>b′, as well as a glass substrate101 can be used efficiently. A relationship a=b may be established aslong as there is no particular problem. Similarly, a relationship a′=b′may be established as long as there is no particular problem. Distance ccan be so set as to satisfy a condition a, a′, b, b′>c.

[0057] As described above, in the manufacture of the active matrixliquid crystal display device, the invention can improve the yield whileefficiently using glass substrates.

What is claimed is:
 1. A method for manufacturing a plurality of displaypanels comprising steps of: arranging a plurality of panel portions overa substrate, each panel portion having a pixel area and at least onedriving circuit area, and positional relationship between the drivingcircuit area and the pixel area being the same in any of the panelportions over said substrate; and dividing said substrate into saidplurality of display panels, wherein a shortest distance between oneside of the substrate and a nearest driving circuit area in one of saidpanel portions is larger than a shortest distance between another sideof the substrate and a nearest pixel area in another one of said panelportions over the substrate.
 2. A method according to claim 1 , whereinsaid one side of the substrate mostly faces driving circuit areas ofsaid panel portions and said another side of the substrate mostly facespixel areas of said panel portions.
 3. A method according to claim 1 ,wherein each display panel constitutes a liquid crystal display device.4. A method according to claim 1 , wherein said pixel areas and saiddriving circuit areas comprise a plurality of thin film transistorsformed over said substrate, each thin film transistor having an activelayer comprising a crystalline semiconductor film formed over saidsubstrate.
 5. A method according to claim 1 , wherein said substratecomprises a material selected from the group consisting of glass,quartz, and resin.
 6. A method according to claim 1 , wherein saidplurality panel portions are arranged in a matrix form over saidsubstrate.
 7. A method according to claim 1 , wherein said one panelportion and said another one panel portion are diagonally arranged oversaid substrate.
 8. A method for manufacturing a plurality of displaypanels comprising steps of: arranging a plurality of panel portions overa substrate, each panel portion having a pixel area and at least onedriving circuit area, and positional relationship between the drivingcircuit area and the pixel area being the same in any of the panelportions over said substrate; and dividing said substrate into saidplurality of display panels, wherein a shortest distance between oneside of the substrate and a driving circuit area in one panel portionlocated nearest to the one side of the substrate is larger than ashortest distance between another side of the substrate and a pixel areain another one panel portion located nearest to the another side of thesubstrate.
 9. A method according to claim 8 , wherein said one side ofthe substrate mostly faces driving circuit areas of said panel portionsand said another side of the substrate mostly faces pixel areas of saidpanel portions.
 10. A method according to claim 8 , wherein each displaypanel constitutes a liquid crystal display device.
 11. A methodaccording to claim 8 , wherein said pixel areas and said driving circuitareas comprise a plurality of thin film transistors formed over saidsubstrate, each thin film transistor having an active layer comprising acrystalline semiconductor film formed over said substrate.
 12. A methodaccording to claim 8 , wherein said substrate comprises a materialselected from the group consisting of glass, quartz, and resin.
 13. Amethod according to claim 8 , wherein said plurality panel portions arearranged in a matrix form over said substrate.
 14. A method according toclaim 8 , wherein said one panel portion and said another one panelportion are diagonally arranged over said substrate.
 15. A method formanufacturing a plurality of display panels comprising steps of:arranging a plurality of panel portions over a substrate, each panelportion having a pixel area and at least one driving circuit area, andpositional relationship between the driving circuit area and the pixelarea being the same in any of the panel portions over said substrate;and dividing said substrate into said plurality of display panels,wherein shortest distances between at least one driving circuit area ofone panel portion and two adjacent sides of the substrate are largerthan shortest distances between a pixel area of another one panelportion and another two adjacent sides of the substrate, and whereinsaid two adjacent sides of the substrate are close to said one panelportion and said another two adjacent sides of the substrate are closeto said another one panel portion.
 16. A method according to claim 15 ,wherein each display panel constitutes a liquid crystal display device.17. A method according to claim 15 , wherein said pixel areas and saiddriving circuit areas comprise a plurality of thin film transistorsformed over said substrate, each thin film transistor having an activelayer comprising a crystalline semiconductor film formed over saidsubstrate.
 18. A method according to claim 15 , wherein said substratecomprises a material selected from the group consisting of glass,quartz, and resin.
 19. A method according to claim 15 , wherein saidplurality panel portions are arranged in a matrix form over saidsubstrate.
 20. A method according to claim 15 , wherein said one panelportion and said another one panel portion are diagonally arranged oversaid substrate.
 21. A method for manufacturing a plurality of displaypanels comprising steps of: arranging a plurality of panel portions overa substrate, each panel portion having a pixel area and at least onedriving circuit area, and positional relationship between the drivingcircuit area and the pixel area being the same in any of the panelportions over said substrate; and dividing said substrate into saidplurality of display panels, wherein shortest distances between at leaston driving circuit area of one panel portion and two adjacent sides ofthe substrate are larger than shortest distances between a pixel area ofanother one panel portion and another two adjacent sides of thesubstrate, and wherein said two adjacent sides of the substrate aremainly facing driving circuit areas of plural panel portions and saidanother two adjacent sides of the substrate are mainly facing pixelareas of plural panel portions.
 22. A method according to claim 21 ,wherein each display panel constitutes a liquid crystal display device.23. A method according to claim 21 , wherein said pixel areas and saiddriving circuit areas comprise a plurality of thin film transistorsformed over said substrate, each thin film transistor having an activelayer comprising a crystalline semiconductor film formed over saidsubstrate.
 24. A method according to claim 21 , wherein said substratecomprises a material selected from the group consisting of glass,quartz, and resin.
 25. A method according to claim 21 , wherein saidplurality panel portions are arranged in a matrix form over saidsubstrate.
 26. A method according to claim 21 , wherein said one panelportion and said another one panel portion are diagonally arranged oversaid substrate.